The discovery of a lipid-linked glucuronide and its synthesis by chicken liver.
Upon incubation with uridine diphosphate-[14C]glucuronic acid, membrane fractions from adult and phenobarbital-induced embryonic liver synthesize a single glucuronide, which is soluble in chloroform:methanol (2:1). The compound is completely hydrolyzed and glucuronic acid released by either mild acid or beta-glucuronidase, whereas mild base hydrolysis results in a mixture of glucuronic acid and glucuronic acid-1,2-cyclic phosphate. These data and the behavior of the lipid-linked glucuronide on DEAE-cellulose chromatography indicate that the compound contains a monophosphate diester of glucuronic acid, which is beta-linked to a lipid. The synthesis of the lipid-linked glucuronide in uninduced normal embryonic liver is very low (5-15 pmol product/mg/5 min) at all developmental ages up to hatching, but the introduction of phenobarbital into the air space of a 9-10-day-old embryo causes a premature increase of activity (75-150 pmol products/mg/5 min) within 7 days. The glucuronyltransferase in adult and induced embryonic liver has a Km for UDPGlcUA of 0.17 x 10(-3) M and a broad pH optimum between pH 6 and 7. Glucuronic acid is released from the lipid-linked glucuronide by a beta-glucuronidase in liver that is active at neutral pH and is not inhibited by saccharolactone. This glycosidase activity appears, therefore, to be distinct from the previously characterized lysosomal beta-glucuronidase. Fractionation of adult chicken liver membranes by differential centrifugation indicates that over 70% of the glucuronyltransferase is associated with the nuclear and mitochondrial fractions. The endogenous beta-glucuronidase capable of hydrolyzing the lipid-linked glucuronide was not separated from the glucuronyl-transferase activity during fractionation. The data available suggests that the lipid-linked glucuronide is involved directly in the generation of free glucuronic acid for further metabolism.
D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000201:enzymology; D002642:Chick Embryo; D002645:Chickens; D005965:Glucuronates / Q000096:biosynthesis* / Q000302:isolation & purification; D005966:Glucuronidase / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D050356:Lipid Metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology*; D010634:Phenobarbital / Q000494:pharmacology; D013347:Subcellular Fractions / Q000201:enzymology; D014535:Uridine Diphosphate Glucuronic Acid
D005965:Glucuronates; D014535:Uridine Diphosphate Glucuronic Acid; D014453:Glucuronosyltransferase; D005966:Glucuronidase; D010634:Phenobarbital